Zero-thickness interface model with chemical degradation by acid attack

Carbon dioxide (CO2) storage in abandoned oil/gas reservoirs is considered a viable alternative to reduce greenhouse gas emissions to the atmosphere. An important element of the risk associated with long-term CO2 storage is the loss of integrity of the cement seals of the abandoned wells in the reservoir. Among others, one possible cause of loss of integrity is the degradation of the oil-well cement due to the acid attack of the carbonated brine in the reservoir. In previous studies, the authors have developed a diffusion-reaction model for simulating this degradation process. In order to study possible coupled Chemo-Mechanical (CM) mechanisms, this model will be coupled with an existing mechanical model. For this purpose, in this paper, an existing constitutive law for zero-thickness interface, based on the theory of elasto-plasticity with concepts of fracture mechanics, is modified to incorporate the effect of chemical degradation on the mechanical strength parameters. Preliminary results obtained with this new constitutive law are presented, in order to illustrate the main aspects of the proposed constitutive law, as well as a possible C-M degradation mechanism that should be considered in the long-term safety assessment of CO2 geological storage projects

¿Qué hacen y qué entienden los estudiantes y profesores de física cuando usan expresiones diferenciales?

En un trabajo previo realizamos una clarifi cación del uso del cálculo diferencial y determinamos un conjunto de indicadores de lo que sería una adecuada comprensión del concepto de diferencial en la física. Guiados por las conclusiones de ese trabajo, presentamos ahora el análisis que hemos realizado de la enseñanza habitual, más concretamente sobre lo que hacen y entienden los estudiantes y profesores cuando usan el cálculo diferencial en las aplicaciones físicas. Después de enunciar y fundamentar la hipótesis de partida, y de presentar el diseño experimental elaborado para someterla a prueba, se muestran y discuten los resultados más importantes que hemos obtenido al aplicar ese diseño con una amplia muestra de profesores de bachillerato y estudiantes de bachillerato y universidad. Esos resultados confirman la ausencia de todos los indicadores de comprensión de la diferencial, poniendo de manifiesto el uso meramente algorítmico del cálculo y las consecuencias negativas que ello tiene para el aprendizaje de la física.One of our previous works explained the use of differential calculus and determined a series of indicators of what could be considered as the appropriate understanding of the concept of differential in physics. Following the conclusions reached in the aforesaid work, this article now analyses common teaching, and more precisely what teachers and students do and understand when applying differential calculus in physics. The present work exposes and justifi es our first hypothesis and presents the experimental design elaborated to test it, and then puts forward the most relevant results registered when applying that design on a large sample of secondary school teachers and secondary school and university students. Attained results prove the absence of all understanding indicators of the differential and highlight the merely logarithmical use made of calculus, as well as the negative impact it has on learning physics

Obstacles to Mathematization in Physics: The Case of the Differential

The process of the mathematization of physical situations through differential calculus requires an understanding of the justification for and the meaning of the differential in the context of physics. In this work, four different conceptions about the differential in physics are identified and assessed according to their utility for the mathematization process. We also present an empirical study to probe the conceptions about the differential that are used by students in physics, as well students’ perceptions of how they are expected to use differential calculus in physics. The results support the claim that students have a quasi-exclusive conception of the differential as an infinitesimal increment and that they perceive that their teachers only expect them to use differential calculus in an algorithmic way, without a sound understanding of what are they doing and why. These results are related to the lack of attention paid by conventional physics teaching to the mathematization process. Finally, some proposals for action are put forward

Diffusion-reaction modelling of the degradation of oil-well cement exposed to carbonated brine

The essential aspects of a diffusion-reaction model in development for the degradation process of oil-well cement exposed to carbonated brine are presented in this paper. The formulation consists of two main diffusion/reaction field equations for the concentrations of aqueous calcium and carbon species in the hardened cement paste pore solution, complemented by a number of chemical kinetics and chemical equilibrium equations. The volume fraction distribution of the solid constituents of the hardened cement paste and the reaction products evolve with the progress of the reaction, determining the diffusivity properties of the material. A sensitivity analysis of some parameters of the model is presented to illustrate the capabilities to reproduce realistically some aspects of the degradation process.Postprint (published version

Effects of the Selected Point of Voltage Reference on the Apparent Power Measurement in Three-Phase Star Systems

[EN] The phenomenon responsible for the different apparent powers measured in a subsystem of a three-phase star-configured system, based on the voltage reference point, was identified in this paper using specific components of the instantaneous powers, as a result of applying the conservation of energy principle to the entire system. The effects of the phenomenon were determined using a proposed apparent power component referred to as the neutral-displacement power, whose square is the quadratic difference between the apparent powers of a subsystem, measured using two voltage reference points. The neutral-displacement power is a component of the apparent power, which is determined using the values of the zero-sequence voltages and the line currents in that subsystem. Expressions of the proposed power were derived using the Buchholz apparent power formulations. The validation of the derived expressions was checked in the laboratory and in a real-world electrical network, using a well-known commercial analyzer and a prototype developed by the authors.This research was funded by Universidad Politecnica de Valencia, under grant Primeros Proyectos de Investigacion (PAID-06-18), Vicerrectorado de Investigacion, Innovacion y Valencia.León-Martínez, V.; Montañana-Romeu, J.; Peñalvo-López, E.; Álvarez, C. (2020). Effects of the Selected Point of Voltage Reference on the Apparent Power Measurement in Three-Phase Star Systems. Applied Sciences. 10(3):1-22. https://doi.org/10.3390/app10031036S122103Emanuel, A. E., & Orr, J. A. (s. f.). The effect of neutral path impedance on voltage and current distortion. Part I. symmetrical and balanced three-phase systems. 2004 11th International Conference on Harmonics and Quality of Power (IEEE Cat. No.04EX951). doi:10.1109/ichqp.2004.1409351Emanuel, A. E., & Orr, J. A. (s. f.). The effect of neutral path impedance on voltage and current distortion. Part II. Imbalanced three-phase systems. 2004 11th International Conference on Harmonics and Quality of Power (IEEE Cat. No.04EX951). doi:10.1109/ichqp.2004.1409350Boyajian, A., & McCarty, O. P. (1931). Physical Nature of Neutral Instability. Transactions of the American Institute of Electrical Engineers, 50(1), 317-327. doi:10.1109/t-aiee.1931.5055789Gates, B. G. (1936). Neutral inversion in power systems. Journal of the Institution of Electrical Engineers, 78(471), 317-325. doi:10.1049/jiee-1.1936.0051Clarke, E., Crary, S. B., & Peterson, H. A. (1939). Overvoltages During Power-System Faults. Transactions of the American Institute of Electrical Engineers, 58(8), 377-385. doi:10.1109/t-aiee.1939.5057977Concordia, C., & Peterson, H. A. (1941). Arcing faults in power systems. Electrical Engineering, 60(6), 340-346. doi:10.1109/ee.1941.6432165Mortlock, J. R., & Dobson, C. M. (1947). Neutral earthing of three-phase systems, with particular reference to large power stations. Journal of the Institution of Electrical Engineers - Part II: Power Engineering, 94(42), 549-568. doi:10.1049/ji-2.1947.0152Rocha, A. C. O., Souza, W. M., & Mendes, J. C. (s. f.). Practical experiences in the analysis of abnormal voltages due to neutral instability. 2004 IEEE/PES Transmision and Distribution Conference and Exposition: Latin America (IEEE Cat. No. 04EX956). doi:10.1109/tdc.2004.1432511Raunig, C., Schmautzer, E., Fickert, L., Achleitner, G., & Obkircher, C. (2009). Displacement voltages in resonant grounded grids caused by capacitive coupling. IET Conference Publications. doi:10.1049/cp.2009.0692Konotop, I., Novitskiy, A., & Westermann, D. (2014). Constraints on the use of local compensation for the correction of neutral voltage displacement caused by the influence of nearby power lines. 2014 Electric Power Quality and Supply Reliability Conference (PQ). doi:10.1109/pq.2014.6866832Kai, L., Guojie, X., Xiaojing, G., Kun, Y., Duohong, C., Ran, L., … Xiangjun, Z. (2018). Method for Suppressing Neutral Point Displacement Overvoltage and Suppression Circuit in Distribution Network. 2018 China International Conference on Electricity Distribution (CICED). doi:10.1109/ciced.2018.8592153Harner, R., & Owen, R. (1971). Neutral Displacement of Ungrounded Capacitor Banks During Switching. IEEE Transactions on Power Apparatus and Systems, PAS-90(4), 1631-1638. doi:10.1109/tpas.1971.293151Jinglu, L., Xin, W., & Chunyan, S. (2006). Discussion on Abnormal Rise of Displacement Voltage of Neutral Point in Compensation Electric Network and its Control Measures. 2006 International Conference on Power System Technology. doi:10.1109/icpst.2006.321700Emanuel, A. E. (2010). Power Definitions and the Physical Mechanism of Power Flow. doi:10.1002/9780470667149Czarnecki, L. S. (1988). Orthogonal decomposition of the currents in a 3-phase nonlinear asymmetrical circuit with a nonsinusoidal voltage source. IEEE Transactions on Instrumentation and Measurement, 37(1), 30-34. doi:10.1109/19.2658Hyosung Kim, Blaabjerg, F., & Bak-Jensen, B. (2002). Spectral analysis of instantaneous powers in single-phase and three-phase systems with use of p-q-r theory. IEEE Transactions on Power Electronics, 17(5), 711-720. doi:10.1109/tpel.2002.802188Willems, J. L., Ghijselen, J. A., & Emanuel, A. E. (2005). The Apparent Power Concept and the IEEE Standard 1459-2000. IEEE Transactions on Power Delivery, 20(2), 876-884. doi:10.1109/tpwrd.2005.844267Fortescue, C. L. (1918). Method of Symmetrical Co-Ordinates Applied to the Solution of Polyphase Networks. Transactions of the American Institute of Electrical Engineers, XXXVII(2), 1027-1140. doi:10.1109/t-aiee.1918.4765570Chroma Programmable AC Power Source 61700 https://www.chromausa.com/product/3-phase-programmable-ac-source-61700/Processor Board PCM-9581 http://advdownload.advantech.com/productfile/Downloadfile4/1-124ET90/PCM-9581_user_manual_Ed2.pdfData Acquisition Board PCI-6220 https://www.ni.com/documentation/en/multifunction-io-device/latest/pci-6220/overview/Voltage Transducer LV 25-P https://www.lem.com/en/lv-25pAC Current Clamp i5sPQ3 https://www.fluke.com/es-es/producto/accesorios/pinzas-de-corriente/fluke-i5spq3Resistances DL1017R https://www.delorenzoglobal.com/image/power-engineering-modules.pd

Effect of long-term pore pressure evolution on the integrity of cement plugs of abandoned oil wells in CCS sites

In the context of Carbon Capture Storage (CCS) in abandoned hydrocarbon reservoirs, a preliminary study of the effects of pore pressure evolution on the integrity of oil-well cement seals is performed. A 2D cross-section of the sealed oil-well system (caprock-external cement sheath-steel casing-cement plug) is analysed along its service-life (injection/production activities and abandonment) using the Finite Element Method with zero-thickness interface elements to represent potential cracks. In particular, these elements are pre-inserted in the analysis in between the contacts of caprock-external cement sheath, external cement sheath-casing and casing-cement plug. The results presented show that, depending on the initial state and range of pressure evolution, the different interfaces considered may open or close in a non-trivial manner during the pressure return process. This seems to indicate the importance of considering carefully the pressure return process and subsequent effective stresses evolution in abandoned reservoirs recycled to CCS, in order to avoid that new cracks in well cement seals may lead to potential CO2 leakage in the storage site.This research is supported by grants BIA2016-76543-R from MEC (Madrid), which includes FEDER funds, and 2017SGR-1153 from AGAUR (Generalitat de Catalunya, Barcelona). The first author thanks the scholarship 2017FI-B00559 received from AGAUR (Generalitat de Catalunya, Barcelona).Postprint (published version

3D zero-thickness interface model for fracture of cement-based materials with chemical degradation

In the framework of the Finite Element Method, zero-thickness interface elements have been widely used to model fracturing processes in quasi-brittle materials in a broad variety of problems. In particular, interface elements equipped with elastoplastic constitutive laws that account for the softening of the material strength parameters due to the fracturing mechanical work has been proved to accurately reproduce observed fracture propagation behaviour in concrete. Along this line, this paper presents the extension of an existing constitutive law of this kind to include the effect of chemical degradation of the material in the formation of fractures. The law is defined in terms of the normal and shear stresses on the average plane of the crack and the corresponding normal and shear relative displacements. A hyperbolic cracking (plastification) surface in the stress state determines the crack initiation. The softening of the cracking surface is governed by two history variables: an internal variable that accounts for the dissipated fracturing (plastic) work, and an external variable to be provided by a chemical degradation model that accounts for the effect of chemical degradation on the strength parameters. After a detailed discussion of the formulation, the main characteristics of the proposed law are illustrated with a number of academic examples for different combinations of mechanical loading and chemical degradation sequences. The model is finally validated against experimental results from the literature consisting of three-point bending tests performed on mortar samples previously exposed to an aggressive solution for different time periods.This research is supported by grants BIA2016-76543-R from MEC (Madrid), Spain, which includes FEDER, Spain funds, and 2017SGR-1153 from AGAUR (Generalitat de Catalunya, Barcelona), Spain. The first author thanks the scholarship 2017FI-B00559 received from AGAUR (Generalitat de Catalunya, Barcelona), Spain.Peer ReviewedPostprint (published version

Enhancing the Thermal Stability of Polypropylene by Blending with Low Amounts of Natural Antioxidants

"This is the peer reviewed version of the following article: Hernández-Fernández, Joaquín, Emilio Rayón, Juan López, and Marina P. Arrieta. 2019. Enhancing the Thermal Stability of Polypropylene by Blending with Low Amounts of Natural Antioxidants. Macromolecular Materials and Engineering 304 (11). Wiley: 1900379. doi:10.1002/mame.201900379, which has been published in final form at https://doi.org/10.1002/mame.201900379. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving."[EN] Natural antioxidants are added in very low amounts to protect a polypropylene (PP) matrix against thermo-oxidative degradation during processing. Thus, PP is melt-blended with caffeic, chlorogenic, trans-ferrulic, and p-coumaric acids, and also with flavone and 3-hydroxyflavone at 0.1 wt% with respect to the PP matrix. Neat PP and PP blended with three traditional antioxidants are prepared for comparison. A complete structural, thermal, and mechanical characterization is conducted. Ferrulic acid and particularly caffeic acid increases the thermal stability, showing also the highest activation energy. The structural changes of PP-based films due to the polymer thermal degradation at high temperature (i.e., 400 degrees C) followed by FTIR reveal that antioxidants effectively delay the thermal degradation process. The wettability and the mechanical performance are also studied to get information regarding the industrial application of such films. While caffeic acid provides a more flexible material, ferrulic acid provides higher water resistance. Finally, AFM-QNM shows that PP with caffeic acid has the highest miscibility.This work was supported by the Spanish Ministry of Economy and Competitiveness (MINECO), PROMADEPCOL (MAT2017-84909-C2-2-R). M.P.A. thanks MINECO for Juan de la Cierva-incorporación postdoctoral contract (FJCI-2017-33536).Hernández-Fernández, J.; Rayón, E.; López-Martínez, J.; Arrieta, MP. (2019). Enhancing the Thermal Stability of Polypropylene by Blending with Low Amounts of Natural Antioxidants. Macromolecular Materials and Engineering. 304(11):1-13. https://doi.org/10.1002/mame.201900379S1133041

Modelling acid attack of oilwell cement exposed to carbonated brine

A diffusion-reaction model for the carbonation process of oilwell cement exposed to carbonated brine under CO2 geological storage conditions is presented. The formulation consists of two main diffusion/reaction field equations for the concentrations of aqueous calcium and carbon species in the pore solution of the hardened cement paste, complemented by two diffusion-only field equations for chloride and alkalis concentrations, and by a number of chemical kinetics and chemical equilibrium equations. The volume fraction distribution of the solid constituents of the hardened cement paste and the reaction products evolve with the progress of the reaction, determining the diffusivity properties of the material. The model is used to simulate experimental tests performed by Duguid and Scherer (2010), leading to promising results indicating that the fundamental aspects of the phenomenon are captured.Peer ReviewedPostprint (author's final draft